BBC Micro Teletext Adapter Manual
"Teletext is a service offered by the BBC and IBA which makes available a wide variety of information through the medium of television. This information could be share prices on the stock market or the latest football results; the possibilities are almost endless.
Teletext information is transmitted from BBC and IBA television transmitters and can be received on a commercial television receiver suitably equipped with a Teletext Adapter unit. The transmitted signal however, unlike a normal television signal, is in digital form which makes it additionally suitable for use with the BBC Microcomputer."